The present invention relates generally to data communication lasers, and more specifically to modulation of arrayed lasers.
Lasers are often used for data communication. Commonly the lasers are distributed feedback (DFB) lasers, although distributed Bragg reflecting (DBR) lasers, vertical cavity surface emitting lasers (VCSELs), and others may be used. The light emitted from lasers is used to form data signals, with light approximate a first level indicating a logical high signal and light approximate a second level, generally a very low level, indicating a logical low signal. The light is generally passed through a fiber optic line as a transmission media to a receiver.
Often the lasers emit light at a constant level, generally a high level, and the light is thereafter modulated to form a data signal. In such instances the modulation is often performed by an external modulator, such as an electro-absorption modulator or a lithium niobate Mach-Zehnder modulator. The use of a separate modulator, however, adds to system cost. Moreover, the benefits to signal quality provided by the use of a separate modulator may be unnecessary in some applications, particularly where length of signal travel is not overly great. An example of such applications would be metro communication rings. In such applications it may be more economical to directly modulate laser operation.
In some applications it is useful to provide multiple lasers on a single substrate. For example, in some applications transmission system reliability is an important consideration, as is transmission system time between failures. Failure of a laser, for example, may result in failure of the transmission system, and lasers may exhibit greater failure rates than other components. Further, in some applications, replacement of failed components may be difficult and time consuming. Accordingly, the use of multiple lasers, with some of the lasers serving as spares in the event of failure of a primary laser, is sometimes beneficial.
At times, multiple lasers may be provided on a single substrate. Providing multiple lasers on a single substrate, forming an array of lasers, is beneficial as manufacture of the lasers may be accomplished in an economical manner, and packaging of the lasers does not require undue space. However, in applications where the laser is directly modulated, modulation of a single laser may be desired. Common methods of directly modulating single lasers may be more difficult when an array of lasers on a common substrate is provided.
The present invention provides photonic devices and circuits for use with photonic devices. In one aspect of the invention a photonic device is provided. The photonic device comprises an array of lasers on a common substrate; a drive switch adapted to selectively provide a current to a laser of the array of lasers; and a data switch coupling the common substrate to a ground based on a high speed data signal received by the data switch.
In another aspect the invention comprises a drive circuit for a tunable laser, the tunable laser comprising an array of lasers configured to lase at different wavelengths, the lasers being provided on a common substrate, light from a single selectable laser being coupled to an optical output using a moveable mirror, the drive circuit operating to modulate the light from a selected laser so as to carry a high speed data signal, the drive circuit comprising a switch coupling the common substrate to a low voltage level when the switch is in a first state, the state of the switch depending on a data signal received by the switch; and a drive switch providing a drive signal to the selected laser, based on a laser selection signal received by the drive switch, the drive signal charging a capacitor coupled to the selected laser, with the capacitor causing the selected laser to lase when the switch couples the common substrate to a low voltage.
In another aspect the invention comprises a drive circuit for a tunable laser, the tunable laser comprising an array of lasers configured to lase at different wavelengths, the lasers being provided on a common substrate, light from a single selectable laser being coupled to an optical output using a moveable mirror, the drive circuit operating to modulate the light from a selected laser so as to carry a high speed data signal, the drive circuit comprising a data line coupling a data signal to the lasers; and a drive switch providing a bias signal to a selected laser, based on a laser selection signal received by the drive switch, the bias signal in combination with the data signal to lase in accordance with the data signal.
In another aspect the invention comprises a photonic device comprising an array of lasers, the lasers being semiconductor diode lasers; a switch to bias one of the lasers with a dc current such that the one of the lasers lases; and means to apply an ac data signal to all of the lasers, whereby current to the one of the lasers is modulated by the ac data signal.
These and other aspects of the invention will be more fully comprehended upon study of this disclosure including the associated figures.